The vaccine adjuvant known as ‘MF59’ [1-3] is a submicron oil-in-water emulsion of squalene, Tween 80, and Span 85. It may also includes citrate ions e.g. 10 mM sodium citrate buffer. The composition of the emulsion by volume can be about 5% squalene, about 0.5% polysorbate 80 and about 0.5% Span 85. The adjuvant is described in more detail in Chapter 10 of ref. 4 and chapter 12 of ref. 5. The oil droplets in MF59 are small enough to be sterile-filtered through a 0.2 μm filter. Because it is an adjuvant for administration to humans (e.g. it is included in the FLUAD™ vaccine) then quality control of the vaccine is particularly important, and lot-to-lot variation has to be controlled within narrow limits. Parameters that are important for MF59 include the mean droplet size in the emulsion, the bioburden, the pH, the visual appearance, and the presence of breakdown products or of common contaminants of its ingredients.
It is an object of the invention to provide further and improved assays for quality control of oil-in-water emulsion adjuvants such as MF59.